Detection distance for a US nickel and quarter

[Ferric Toes]

Back to the main subject of the thread. After further tests and comparisons with 'normal' and 'long' sample pulses, I have returned to the normal ones as being best. i.e. in the range 20 - 50uS. Samples of 100uS and upwards appears to give more signal on higher conductivity coins, but the benefit was outweighed by increased noise. Even with increased integrator TC, this was so. The best benefit appeared to be had by lengthening the TX pulse to 350uS.

Eric.

[green]

Back to the main subject of the thread. After further tests and comparisons with 'normal' and 'long' sample pulses, I have returned to the normal ones as being best. i.e. in the range 20 - 50uS. Samples of 100uS and upwards appears to give more signal on higher conductivity coins, but the benefit was outweighed by increased noise. Even with increased integrator TC, this was so. The best benefit appeared to be had by lengthening the TX pulse to 350uS.

Eric.

Interesting. Are you still using integrator https://www.geotech1.com/forums/atta...1&d=1590237972 reply #55. How much did you increase the integrator TC? Are you looking at integrator out with a scope to compare changes or something different?

[liudengyuan]

Don't play these analog circuits anymore, it can't make an excellent machine. A single-chip microcomputer plus high-speed ADC is simple and effective, which can save a lot of cumbersome circuits

[green]

Starting to draw schematic for testing the large coils I'm making to see if I can detect a quarter at 24inches. Compared integrator I used for my last bench circuit and Eric's reply #55. What should integrator out waveform look like when target is swept across the coil? I look at point (a) with a voltmeter when plotting static targets and point (out) for sweeping targets.

Should have cut gain= 10 from the simulations.

Probably for bench testing it doesn't matter. What should it look like for a detector?

[Carl-NC]

Point 'a' should look like a Gaussian curve, as in the upper-left plot. 'out' is the first derivative of 'a', and again the upper-left plot show a classic response curve.

Question: did you intend U2 to invert the preamp signal? R8 is grounded.

[green]

Point 'a' should look like a Gaussian curve, as in the upper-left plot. 'out' is the first derivative of 'a', and again the upper-left plot show a classic response curve.

Question: did you intend U2 to invert the preamp signal? R8 is grounded.

U2 was the invert signal in another analysis (EF sample). Grounded it so I was just looking at a target signal.